This invention relates to electrical lighting systems and more particularly to an improved device for mounting and supplying electrical power to luminaires such as indoor industrial lighting fixtures of the type using high intensity discharge lamps.
Interior industrial lighting is often provided with luminaires containing high intensity discharge (HID) lamps, such as mercury lamps, metal halide lamps or high pressure sodium lamps. Luminaires of this type typically consist of a ballast housing containing a ballast circuit for energizing the lamp and a downwardly directed reflector mounted on the ballast housing. One typical method for installing lighting fixtures of this type is to attach the ballast housing to a junction box which is in turn anchored to a building structure. Wiring within the junction box is then permanently connected to the ballast circuit for supplying power to the lamp. The junction box is mounted, for example, by a rod or pendent having an upper end anchored to the building structure and a lower end which threadably engages the junction box. Or, the junction box can be attached directly with bolts to the building structure or to an I beam or other member within the building. Problems occur with a luminaire installation of this type when it is necessary to change the location of the luminaires or to remove a luminaire, for example, for repair or maintenance. Power is typically supplied in a hard wired branch circuit which connects from fixture junction box to fixture junction box for a number of luminaires. When one of the luminaires in the circuit is to be disconnected, the wiring must be changed manually by an electrician. The wiring also must be changed manually when it is necessary to change switching for selected ones of a number of luminaires in a circuit or to relocate one or more luminaires as lighting requirements change. Since the circuit is permanently connected from fixture to fixture, considerable difficulty and expense is encountered in modifying the circuit connections to selected fixtures.
U.S. Pat. No. 4,001,571, for example, discloses a relocatable lighting system in which power is supplied to a plurality of lighting fixtures through a branch circuit. The branch circuit is formed by branch circuit cables which connect from fixture to fixture. Any fixture can be disconnected from the circuit without removing power from the circuit. However, the system of this patent does not deal with problems relating to both mounting and supplying power to industrial luminaires in a relocatable system.
Luminaires for high intensity discharge lamps often are designed to illuminate the largest possible area without providing high angle glare. High angle glare occurs when the lamp is located within the normal field of vision of a person standing below and to one side of the luminaire. When the luminaire is designed for illuminating a maximum work area, it is important that the luminaire be mounted with a vertical orientation. If the luminaire is inclined by only a small amount, such as about 5.degree., undesirable high angle glare may occur. This inclination will also interrupt the total uniformity of the lighting layout in a work area beneath the luminaire.